Study On The Morphology Of The Carbides In High Chromium Cast Iron

In the present paper, the high temperature gradient directional solidification apparatus with liquid metal cooling (LMC) has been used to study the influence on the precipitation behavior of both primary and eutectic carbides with different solidification rate and alloying elements. Longitudinal and transverse metallographic specimens for microscopic observation have been prepared using conventional techniques. The morphology evolution was observed with NikonEPIPHOT300 metal scope and KYKY-AMRAY1000B SEM. The size, volume fraction and spacing of M7C3 fibers have been measured with SISC-LAS instrument. JEM-2010F TEM is used to observe M7C3 phase. On these bases, the effect of solidification rate on the solidified microstructures such as size of primary M7C3 phase, volume fraction of primary M₇C₃ phase and average spacing of eutectic M₇C₃ phase are systematically investigated in the present paper. The relationship between solidification processing factors and solidification microstructures have been discussed and established.Morphology and mechanical property of directional solidified Fe-Cr-C hypereutectic alloy (3.51%C-30.8%Cr) have been studied. The results show that the alloy consists of Fe-Cr matrix, M7C3 and trace amounts of γ; After directional solidification, carbide fibers are regularly aligned in one direction; The carbides grow along with the direction of [150] and the matrix grows along with the direction of [110]; Primary carbides and eutectic carbides are M₇C₃-type carbides; Primary carbides grow in the manner of outflanking and the transverse section of primary carbides is hexagonal; With the increase of solidification rate, the size and volume fraction of primary carbides will be decreased; The microhardness of transverse section of primary carbides is about HV2000, while that of longitudinal section of primary carbides is about HV1450. With the increase of solidification rate, the tensile strength of Fe-Cr-C hypereutectic alloy decreases first, then increases and finally drops sharply. The maximum tensile strength is 1913MPa with the solidification rate of 15μm/s.Fe-Cr-C-V hypereutectic alloy (3.51%C-30.8%C-1.03%V) and Fe-Cr-C-RE eutectic alloy also consist of Fe-Cr matrix, M7C3 and trace amounts of γ ; According to EDS analysis, Element V which exists mainly in the M7C3 carbides can refine primary carbides as the nucleation particles; RE which exists mainly in the matrix can refine...